1. Field of the Invention
The instant invention relates to an apparatus for power IC heat sinking which provides positioning and clamping forces using the housing assembly for direct mounting heat sinking. In accordance with the instant invention, the electrical components are not heat sunk until the first half of the housing assembly is attached to the circuit board or to the second half of the housing assembly.
2. Description of Related Art
Most electrical components generate thermal energy. Some components generate so much heat that the component itself may be damaged or may operate improperly unless excess thermal energy is removed during operation. Mechanical and thermal contact assemblies in the form of heat sinks of various forms are conventionally used to protect electronic devices from excess heat. Typically, mechanical and thermal contact assemblies require additional mounting structures, such as rivets, screws, or other hardware, to attach or contact the electrical component to the heat sink. In an effort to eliminate the additional mounting structures, the prior art teaches the use of spring clips to attach the electronic components to the heat sink(s).
Generally, there are two apparatuses presently used for mounting the heat generating electrical components to a heat sink. The first apparatus mounts the component in a conventional manner to the heat sink (parts stand perpendicular to the circuit board) and the necessary normal forces are provided by a plastic clamp, compressing the component to the heat sink. An example of this apparatus is shown in FIG. 1. However, the apparatus of FIG. 1 requires additional fasteners which increases assembly time. Over time these fasteners may become disengaged thus reducing heat transfer efficiency. The heat sink apparatus of FIG. 1 is often not a portion of the housing. Hence, an indirect thermal path is created as thermal energy is dissipated from the components to the intermediate heat sink, such as an internal heat rail or bracket, and then to the final heat sink, typically the housing assembly.
As shown in FIGS. 1 and 2, conventional heat sink arrangements require clamps 2 and fasteners 4 to attach the electrical component 1 to the heat sink 6. As shown in FIG. 3, this arrangement sandwiches the heat generating component 1 between the clamp 2 and the heat sink 6 to ensure proper thermal contact therewith. This arrangement incurs the drawback of increased assembly time and often results in the loss of proper thermal contact when the fasteners become disengaged.
A second apparatus places the electrical components directly in contact with the housing assembly, referred to as alternate lead form (ALF) mounting, and the necessary clamping forces are generated when the joining housing portions are fastened together. An example of this prior art is shown in FIG. 4.
FIG. 4 illustrates a conventional arrangement whereby the heat generating component 1 is positioned on its back on the circuit board 11, and the housing 13 provides the clamping force to ensure proper thermal contact between the component and the heat sink. However, this second apparatus serves to greatly reduce the usable circuit board area after assembly.
U.S. Pat. No. 4,923,179 issued on May 8, 1990 to C. Mikolajczak also discloses an electrical component assembly with a heat sink for providing the assembly with a resilient biasing member for improving the thermal contact between the heat generating components and the housing. However, the interior wall utilized by Mikolajczak creates a thermal bottleneck, and the resilient biasing member is likely to relax over time, thus allowing the clamping forces on the components to be reduced.
U.S. Pat. No. 4,167,031 issued on Sep. 4, 1979 to P. D. Patel discloses a heat sink assembly being clamped to the housing via a screw or threaded bolt. The use of the metal holder member creates an intermediate thermal path which is not present when the components are in direct contact with the housing, and there is no provision for adjusting the clamping forces exerted on the components.